Horizontal broad-band omnidirectional antenna



United States Patent 3,534,372 HORIZONTAL BROAD-BAND OMNIDIRECTIONAL ANTENNA Friedrich Scheuerecker, Baldham, and Axel Stark, Gmund,

Germany, assignors to Rohde & Schwarz, Munich, Germany, a corporation of Germany Filed Dec. 22, 1967, Ser. No. 693,000 Claims priority, application Germany, Jan. 3, 1967, 1,541,549 Int. Cl. H01g 11/10, 11/14 US. Cl. 343-742 Claims ABSTRACT OF THE DISCLOSURE A log periodic horizontal broad-band omnidirectional antenna comprising a plurality of concentric loops which are connected in series or parallel and spaced in accordance with the log periodic principle so as to produce an antenna which is omnidirectional and capable of radiating over a broad frequency range.

BACKGROUND OF THE INVENTION Field of the invention An antenna which comprises a plurality of concentrically mounted half-wave loops spaced from each other in accordance with a log periodic principle and omnidirectional is disclosed. The loops are preferably connected in series or alternatively may be connected in parallel.

Description of the prior art SUMMARY OF THE INVENTION The present invention provides a horizontal omnidirectional antenna capable of covering a large bandwidth which is small. This is achieved by mounting a plurality of half-wave dipole loops concentrically in one or more superimposed horizontal planes and with the dimensions of the loops being selected in accordance with the log periodic principle.

The loops are connected to a common feed point preferably in series. If they are connected in parallel, suitable means such as de-coupling capacitor must be provided for each loop so that the individual loops do not short-circuit each other. The dimensions of the loops follow the logarithmic periodic principle. The following formula gives this relationship:

where X is the half diameter of a loop, i.e. the distance of a side limb of the loop from the center and L is the peripheral length of the loop. The loops could have any desired shape, for example circular, rectangular or square, triangular, polygonal or elliptical. Where, in certain cases, it is desired that the radiation should also include a vertical component, the dipole loop could be mounted above the ground in a plane which is inclined to the horizontal.

If a horizontal loop dipole antenna constructed in accordance with the invention and following the logarithmic periodic principle is mounted at a height above the ground about a quarter wavelength, and with the loop peripheral length being a half a wavelength, the real part of the antenna impedance at the feed point is generally of the same order of magnitude of the impedance of the feed cable. In many modes of use, especially with transportable antenna installations, it is very difiicult to mount the assembly at a height of quarter wavelength above the ground and at least three relatively high masts are required. According to a further feature of the invention, the relative height of the antenna above the ground can be reduced by mounting it at a height less than one-tenth of a wavelength above the ground. Also, the peripheral lengths of the dipole loops are reduced in comparison with their normal half wavelength dimensions in such a manner that the input impedance of the antenna is still substantially real (resistive). The input impedance can be regarded as substantially real (i.e. resistive) when a standing wave ratio not greater than 2 is maintained, for example. If the real antenna input impedance is still not equal in magnitude to the impedance of the feeder, a matching transformer can be connected between the antenna and the feeder in a manner well known. The peripheral lengths of the loops and their height above the ground may be of such dimensions that a real antenna impedance is obtained from the value of the feeder impedance. Furthermore, the ratio of the spacing above ground to the length of a loop can be made equal for all the loops so that an antenna is obtained having loops in several mutually parallel planes. In order to improve still further the matching of the input impedance to the impedance of the feeder, it is possible further to connect an additional loop in series with that loop for the lowest frequency. The peripheral dimensions and diameter of this loop would depart from the logarithmic periodic ratio.

Thus, a broad-band omnidirectional antenna can be constructed in accordance with this invention which is mounted close to the ground or it can indeed be laid directly on the ground or buried in the ground. The length of a side of a square loop arrangement for such an antenna for the range covering from 3 to 30 mHz. would only be about 12 meters.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of the antenna according to this invention;

FIG. 2 is a plan view of a modification of the invention;

FIG. 3 is a plan view of a further modification of the invention;

FIG. 4 is a plan view of an additional modification of the invention;

FIG. 5 is a plan view of a further modification of the invention; and

FIG. 6 is a side plan view of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates an antenna according to this invention which comprises a plurality of concentric dipole loops 1, 2, 3 and 4 which are mounted in a horizontal plane or planes. The loops are made of conductors having lengths equal to one-half wavelengths of their operating frequencies. Each loop is thus tuned to a particular frequency and the array covers a broad range of frequencies. The length of the conductors which form 1, 2, 3, 4 are designated L L L and L respectively.

The loops are symmetrically mounted relative to reference lines AB and CD and the distance from line AB to each loop is designated X X X and X respectively.

The distances L and X are related in a log periodic manner according to the formula:

Input terminals E and E are near the center M of the antenna. The loops are connected in series in FIG. 1 with the second end of loop 1 connected by jumper 10 to the first end of loop 3. The second end of loop 3 is connected to the second end of loop 4 by lead 11. The first end of loop 4 is connected by lead 12 to the second end of loop 2 and the first end of loop 2 is connected to feed terminal B In the above description the first portion of the loops are defined as being on the right side of line CD in FIG. 1 and the second portions are on the left side of the line CD. A transformer 50 may be connected to input terminals E1 and E2 to match the irnepdance of the antenna to the input.

FIG. 2 illustrates a modification wherein the first half of loop 1 is connected to one end of the first half of loop 2 by jumper 13 and the second end of the first half of loop 2 is connected to one end of the first half of loop 3 by conductor 14. The other end of the first half of loop 3 is connected by jumper 16 to one end of the first half of loop 4. The other end of the first half of loop 4 is connected to the second half of loop 4. The other end of the second half of loop 4 is connected by lead 17 to one end of the second half of loop 3. The other end of the second half of loop 3 is connected by lead 18 to one end of the second half of loop 2 and the other end of the second half of loop 2 is connected by jumper 19 to the second half of loop 1. The other end of the second half of loop 1 is connected to terminal E FIG. 3 illustrates another manner of connecting loops 14 by jumpers 21, 22, 23, 24, 26 and 27. Generally the first half of each loop is connected to the second half of the adjacent loop as shown.

FIG. 4 illustrates an antenna formed of a coaxial cable having an outer conductor 6 and an inner conductor 7.

A conductor 8 is connected at point E to the center conductor 7 and the coaxial cable and conductor 8 are formed into loops 31, 32 and 33 as shown. Point P of conductor 8 is attached to the outer conductor 6 of the coaxial cable.

The coaxial cable 6 forms the left (relative to FIG. 4) half of loops 33 and 31 and the right half of loop 32.

FIG. illustrates the antenna of FIG. 4 with an additional loop 5 to improve performance at the lower frequency end of the antenna. Although loop 5 has a greater length 1. and X than loop 4, it is not related by the ratio 'r as are loops 1-4 but has a ratio between V;

and {/1 FIG. 6 illustrates the antenna of this invention in which the spacing of the loops above ground are diiferent. For

example, the ratio of the spacing above ground of the loops can be made equal for all the loops so that an antenna is obtained which has loops with varying heights.

In operation, the antenna according to this invention is connected to a suitable feed line for receiving or transmitting energy. The antenna are broad-band and exhibit superior radiation characteristics.

The principles of the invention explained in connection with the specific exemplifications thereon will suggest many other applications and modifications of the same. It is accordingly desired that in construing the breadth of the appended claims they shall not be limited to the specific details shown and described in connection with the exemplifications thereof.

We claim:

1. A horizontal broad-band omnidirectional antenna comprising a plurality of concentric half-wave dipole loops mounted horizontally above the ground an connected to a common feed point, the peripheral lengths and diameters of the loops being related in steps on accordance with the logarithmic periodic principle according to the relation ship n-H. n+1 X L,

where X is the half diameter of a loop and L is the peripheral length of a loop, X is the half diameter of an adjacent loop and L is the peripheral length of an adjacent loop.

2. A horizontal broad-band omnidirectional antenna according to claim 1, in which the dipole loops are mounted at a height above the ground of less than ,4 of the maximum operating wavelength and the peripheral lengths of the dipole loops are reduced in comparison with the normal half wavelength dimension in such a manner that the antenna input impedance is substantially real.

3. A horizontal broad-band omnidirectional antenna according to claim 2, in which a transformer is interposed at the feed point to match the substantially real antenna input impedance to the impedance feed line.

4. A horizontal broad-band omnidirectional antenna according to claim 2, in which the peripheral lengths of the loops and their heights above the ground are of such dimensions that the input impedance is real.

5. A horizontal broad-band omnidirectional antenna according to claim 1 in which the ratio of the distance above the ground to the length of a loop is the same for each of the loops.

6. A horizontal broad-band omnidirectional antenna according to claim 1 having an additional loop with a peripheral length and diameter which does not follow the logarithmic periodic ratio.

7. An antenna according to claim 1 wherein the loops are connected in series.

8. An antenna according to claim 1 wherein the loops are divided into first and second portions and the first and second portions of the loops are connected together by jumpers to form a composite antenna.

9. An antenna according to claim 8 wherein first portions of one loop are connected to first portions of other loops.

10. An antenna according to claim 8 wherein first portions of one loop are connected to second portions of other loops.

References Cited UNITED STATES PATENTS 3,267,479 8/1966 Smith et al. 343-806 HERMAN K. SAALBACH, Primary Examiner M. NUSSBAUM, Assistant Examiner U.S. Cl. X.R. 

